When the name in the database is different from the name used in the script
When the name in the request is different from the name used in the script

$fdx[ 'username' ] = array(
	"label"=>$lng[ 'username' ],
	"dname"=>"usernamex",
	"rname"=>"usernamey",

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$fs->get( "first_name!html" ); //specify output type
$fs->get( "first_name.label" ); //specify data type